The inventive subject matter relates to electrical apparatus and methods of operating the same and, more particularly, to apparatus and methods for controlling transformers.
Electrical loads are commonly connected to a power distribution system using transformers. For example, commercial and residential loads are typically connected to the electrical grid using transformers that provide a reduced voltage to premises equipment from relatively high voltages that are used in the distribution system. Transformers may also be used to provide isolation between a power source and a load. For example, industrial electrical equipment, such as adjustable frequency motor drives, may include input transformers that are used to provide isolation for drive electronics.
Relatively large inrush currents may develop when such transformers are initially connected to a power source using a contactor or similar switching device. These inrush currents can be several times greater than the currents generated at steady state, and can cause circuit interruption devices, such as circuit breakers or fuses, to inadvertently operate. Techniques for reducing such inrush currents by pre-energizing a transformer via a high-impedance source are described, for example, in U.S. Pat. No. 9,337,762 to Gibbs et al.